Protective boot for automotive component and method of making

ABSTRACT

A blow molded product which is generally tubular having a first and second open ends, a bellows section intermediate said first and second ends so that the product is flexible, and a skirt adjacent the second end, the skirt having an outer cylindrical outer surface and a lobed inner surface. The bellows section is formed in a blow molding operation and the skirt is formed by injection molding. The final product is formed by thermally fusing the two portions together. This process enables molding of a product with an external surface which may substantially cylindrical with an internal surface which has lobes, or other internal projections or non-cylindrical surface.

This application is a divisional of U.S. Application Ser. No. 08/995,408filed Dec. 17, 1997 now U.S. Pat. No. 6,099,788.

FIELD OF THE INVENTION

This invention relates generally to protective boots for automobilecomponents, and particularly to a protective boot for a constantvelocity joint.

BACKGROUND OF THE INVENTION

Blow molding is a well-known technique used for manufacturing hollowplastic protective boots for automobile components. However, such bootstypically have a complex shape which can present difficulties to blowmolding such an article.

Protective boots used on automobile components, such as a boot for aconstant velocity joint (CVJ), perform several functions includingprotecting the joint from outside dirt and debris, as well asmaintaining lubricant around the joint. Many protective boots, however,must attach to automotive components which do not have a cylindricalexternal configuration to which the boot may be clamped. For example,due to the bearing configuration of typical constant velocity joints,the shaft to which one end of a CVJ boot must clamp is lobed, ratherthan cylindrical. Thus, in order to perform its protective functionsproperly, a CVJ boot requires a seal or bushing element at one end to beclamped between the boot and the shaft. The bushing has a tri-lobedinternal configuration.

In use, however, the addition of this extra element increases the waysin which the protective boot may fail. For example, if there is anincomplete seal between the bushing and the boot, lubricant may beallowed to escape from the joint or contaminants allowed to enter.

Accordingly, there is a need for a single piece boot and bushing whichprovides a suitable external clamping surface and an internal irregularsurface which can be configured to meet the requirements of a mechanicalstructure in association with which the product is to be used. Producingsuch a product is very difficult using conventional blow moldingtechniques. Conventional blow molding techniques cannot be used tocomprise a lobed internal surface on a portion having a cylindricalouter surface because thermoplastic material spreads out evenly underthe effect of blowing pressure in typical blow molding.

A technique which overcomes this problem is disclosed in the applicant'sco-pending U.S. Pat. Application Ser. No. 08/694,234, filed Aug. 8,1996, now U.S. Pat. No. 5,900,205, which is incorporated herein byreference. That application discloses a combined blow molding andcompression molding technique in which a parison is confined in a moldand, prior to blowing, a core is introduced into the mold to movethermoplastic material axially, radially and circumferentially to forman integral boot and lobed bushing product. The method disclosed in thatapplication has the limitation, however, that only a certain amount ofthermoplastic material may be. moved by the introduction of a core orslides into a mold prior to blow molding, thus limiting the size oflobes which may be formed on a bushing portion of an integral bushingand boot.

Accordingly, there is a need for a process which is capable of moldingan integral thermoplastic boot and bushing having unlimited lobe size orhaving other non-cylindrical internal surface.

SUMMARY OF THE INVENTION

The present invention provides an improved protective boot for anautomotive component and a method of making. In one aspect the inventionprovides a thermoplastic protective boot for an automotive componenthaving an integral bushing, comprising:

a boot element, the boot element having a first portion with a generallycylindrical outer surface for engaging with a circular clamp; and

a bushing element, the bushing element having a generally cylindricalwall portion and a plurality of lobed portions, the wall portion havinga thickness, the lobed portions projecting inwardly from the wallportion a distance of at least four (4) times the thickness of the wallportion.

In another aspect the invention provides a protective boot assembly foran automobile component comprising:

a generally tubular body having first and second open ends, the bodyhaving a flexible bellows-shaped portion intermediate the first andsecond ends, the first end comprising a skirt portion, the skirt portionbeing defined by a generally cylindrical first wall, the first wallhaving inner and outer surfaces, the outer surface being generallycylindrical for engaging a circular clamp, the outer surface having aplurality of projections projecting outwardly from the first wall at thefirst end for retaining a circular clamp, the boot having one or moreprojections projecting inwardly of the first wall, the second endcomprising a neck portion, the neck portion being defined by a generallycylindrical second wall, the second wall having a generally cylindricalouter surface for engaging a circular clamp, the outer surface having aplurality of projections projecting outwardly from the second wall atthe second end for retaining a circular clamp; and

two circular clamps, wherein one of the clamps is located around theboot at the skirt portion and one of the clamps is located around theboot at the neck portion and the clamps are retained in place by theprojections.

In a third aspect the invention provides a method of producing athermoplastic protective boot for an automotive component having anintegral bushing comprising:

forming a boot element having a first portion, the first portion havinga generally cylindrical first wall with an inner and outer surface, thefirst wall having a first diameter at the inner surface;

forming a bushing element having a generally cylindrical second wallwith an inner and outer surface, the second wall having a seconddiameter at the outer surface, the second diameter being approximatelyequal to the first diameter of the boot element, the inner surface ofthe bushing element having one or more projections inwardly of thesecond wall;

positioning the bushing element within the boot element so that theouter surface of the bushing element is substantially in contact withthe inner surface of the boot element; and

integrating the boot element and the bushing element by thermally fusingthe elements together.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show moreclearly how it may be carried into effect, reference will now be made byway of example to the accompanying drawings.

The drawings show a preferred embodiment of the present invention, inwhich:

FIG. 1 shows a perspective view of a CVJ boot according to the presentinvention;

FIG. 2 shows a cross sectional side view of a typical boot of the priorart with a conventional bushing installed therein;

FIG. 3 shows a plan view of a typical bushing of the prior art;

FIG. 4 shows a perspective view of the components, prior to assembly, ofthe boot of FIG. 1;

FIG. 5 is a perspective view of an assembly of the boot of FIG. 1, withencircling clamps installed thereon;

FIGS. 6 and 7 illustrate, diagrammatically, the steps of producing theboot of FIG. 1 in accordance with one aspect of the invention;

FIGS. 8 through 14 illustrate, diagrammatically, the steps of making theboot of FIG. 1 in accordance with an alternate embodiment of theinvention;

FIG. 15 shows an end view of the integral boot and bushing of the priorart; and

FIG. 16 shows an end view of the boot of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, an automotive boot according to the presentinvention is indicated generally at 10. Boot 10 has a neck 12, a bellows14 and a skirt 16. The skirt 16 is a generally cylindrical wall. Neck 12and skirt 16 have generally cylindrical external surfaces 13 and 17 toaccommodate, in use, encircling clamps, sometimes referred to as hoseclamps, which will attach externally thereto to install boot 10 on aconstant velocity joint. Projecting radially outwardly from surface 13of neck 12 and surface 17 of skirt 16 are a series of retainer ribs 15and 19, respectively. The function of retainer ribs 15 and 19 will bediscussed below. An internal surface 18 of skirt 16 is generallycylindrical but has three lobes 20 extending radially inwardly fromskirt 16.

Referring now to FIG. 2, a CVJ boot in accordance with the prior art isshown generally at 30. Boot 30 has a neck 32, a bellows 34 and a skirt36. As with boot 10, neck 32 and skirt 36 have generally cylindricalexternal surfaces. An internal surface 38 of skirt 36 is cylindrical toaccommodate a seal or bushing 40.

Referring to FIG. 3, a bushing 40 according to the prior art is shown.Bushing 40 has a cylindrical outer surface 42 and an inner surface 44having several lobed portions 46. As described above, traditionally,bushing 40 is required because the bearings of a constant velocityjoint, to which skirt 36 must be damped, are non-cylindrical.

In use, the bushing 40 and the boot 30 are installed on a constantvelocity joint (not shown). The constant velocity joint includes twoshaft-like elements, one having a diameter nominally equal to the innerdiameter of neck 32 and the other end having a diameter nominally equalto the inner diameter of bushing 40. Hose clamps (not shown) areattached externally over neck 32 and skirt 38. The clamps are tightenedagainst the structure of the joint to form a tight seal so thatlubricant contained within the boot 30 may not escape. The flexiblebellows 34 accommodates the relative angular movement of the structuralportions of the constant velocity joint. Bushing 40 is installed inskirt 36 with outer surface 42 in contact with internal surface 38 ofboot 30. The clamps are then placed around neck 32 and skirt 38 andtightened appropriately to assemble boot 30 to the constant velocityjoint. Referring again to FIG. 2, when so installed there may be aspace, indicated generally at S, at some point or points between skirt36 and bushing 40 through which lubricant may leak or through whichoutside debris or fluids may enter to contaminate the lubricant insideboot 30. The size of any such space S depends on the tolerances to whichboot 30 and bushing 40 are manufactured, the amount of wear on boot 30and bushing 40, and the of clamping pressure applied by the clamp.

Referring to FIG. 5, in use, boot 10 according to the present inventionis installed on a constant velocity joint (not shown) and is clamped ina similar fashion as boot 30 of the prior art, with hose clamps 22 and24 at neck 12 and skirt 16, respectively, creating an assembly 100.Retainer ribs 15, 19 serve to retain in place a hose clamp 22 on neck 12and a hose clamp 24 on skirt 16. Clamps 22 and 24 are tightened againstthe structure of the joint to form a tight seal so that lubricantcontained within the boot 10 may not escape. Unlike boot 30 of the priorart, there is no space S between the bushing element and the skirtelement of assembly 100 because boot 10 is an integral boot and bushing.

Advantageously, retainer ribs 15 and 19 also hold clamps 22 and 24 inplace prior to tightening the clamps. Assembly 100 is thus completelyready to be assembled to a constant velocity joint as a single assembly.This eliminates the necessity of stocking and assembling at theautomotive factory a separate inventory of clamps, boot portions andbushing portions. Rather only a single assembly 100 is required at theautomotive factory, with considerable economic advantage to theautomotive factory.

The steps which may be employed to manufacture the boot 10 are showndiagrammatically in FIGS. 4 and 6 through 12. Boot 10 is formedgenerally in a 3-step process. Referring to FIG. 4, this processcomprises, generally, blow molding a boot portion 50, injection moldinga bushing portion 52, inserting bushing portion 52 into boot portion 50and thermally welding the two together.

According to one embodiment of the present method, boot portion 50 andbushing portion 52 are molded separately. Referring to FIG. 4, bootportion 50 is formed using a typical blow molding technique for moldingsimilarly shaped articles, and may be molded identically to boot 30 ofthe prior art. Boot portion 50 comprises neck 12, bellows 14 and skirt16. The skirt 16 is a generally cylindrical wall. The skirt 16 has agenerally cylindrical surface 17. The internal surface 18 of skirt 16 ispreferably generally cylindrical.

Bushing portion 52 is formed separately from boot portion 50, usingconventional injection molding techniques. Although injection molding ispreferred, it will be appreciated that other methods of forming bushingportion 52 may be used. Bushing portion 52 has an outer cylindricalsurface 54 and internal surface 18 with lobes 20, shaped to matingly fitwith the constant velocity joint with which the boot 10 is to be used.The outside diameter of bushing portion 52 is preferably the same as theinside diameter of skirt 16.

Referring now to FIG. 6, boot portion 50 and bushing portion 52 arejoined in one aspect of the present method by spin welding. Boot portion50 and bushing portion 52 are placed in a milling machine 56, or thelike, and held at locations 58. Bushing portion 52 is then insertedinside skirt 16, as shown in FIG. 7, so that outer surface 54 of bushingportion 52 is in contact with internal surface 18 of skirt 16. The partsare then spun, relative to one another, the friction at surfaces 18 and54 creating heat. The heat at least partially melts surfaces 18 and 54.When sufficient melting has occurred, the spinning is stopped and theparts are allowed to freeze, thereby fusing together. The bushingportion 52 and the boot portion 50 consequently form the integral boot10.

Referring to FIGS. 8 to 14, in an alternate embodiment of the presentmethod bushing portion 52 is first injection molded and boot portion 50is then blow molded around bushing portion 52, embedding it therein.

Referring to FIG. 8, a typical blow mold is illustrated generally at 60.The mold 60 comprises partible mold halves 62 and 64. In order toprovide a bellows-like configuration to the blow molded article, themold halves 62 and 64 are made up of a plurality of segments. Thesesegments are shown at 62A, 62B, 62C, 62D, 62E, 62F, 62G, 62H, andsimilar segments shown at 64A through H. The segments A through H ofeach of the mold halves 62 and 64 are fixed to one another and move as aunit. The mold halves 62 and 64 each comprise a moving slide 66 and 68respectively. The slides 66 and 68 may be moved independently of thesections 62A through H and 64A through H by means of cylinder 70 and 72respectively. The mold 60 is a conventional mold which may be used tomanufacture boots of prior art configuration as well as the bootportions 50 of this invention. Mold 60 is contoured, in a conventionalmanner, at segments 62 a, 64 a and slides 66, 68, respectively, so thatretainer ribs 15 and 19 will be formed on neck 12 and skirt 16 of bootportion 50. Located below the mold halves 62 and 64, there is a supportpedestal illustrated generally at 80. The support pedestal 80 comprisesa movable core 82 which contains a movable blow pin 84 and a support 85for previously injection molded bushing portion 52. The support pedestalalso includes a cylinder 86 which moves core 82 vertically relative tosupport pedestal 80. Support pedestal 80 also comprises a pair offingers 88 which are movable relative to one another and to pedestal 80in the horizontal direction.

Support pedestal 80 is located vertically below an extrusion head (notshown). Positioned on support 85 of core 82 is a previously injectionmolded bushing portion 52. Mold halves 62 and 64, when in the openposition, permit the extrusion of a parison 90 therebetween with theparison 90 extending downwardly toward support pedestal 80.

At the commencement of the procedure in accordance with this invention,mold halves 62 and 64 are in their open position. Fingers 88 are drawninwardly to their starting position.

With all mechanical parts as shown in FIG. 8, the first step in theprocess is extruding of parison 90 from the extrusion head. The parisonis relatively small in diameter and hangs vertically from the extrusionhead, as shown in FIG. 8. The placement of fingers 88 is such that aparison drops over the fingers, the internal diameter of parison 90 islarger than the spacing between fingers 88.

FIG. 9 shows the second stage in the process. Fingers 88 movehorizontally outwardly to create a relatively large diameter opening inparison 90. Mold halves 62 and 64 have been closed to the finalposition.

FIG. 10 shows cylinder 86 having extended, moving core 82 verticallyupwardly between fingers 88 and internally to parison 90. Core 82, withbushing portion 52 in place thereon, stops in the position shown in FIG.10. Bushing portion 52, when placed in contact with molten parison 90,partially melts along surfaces 54 which is in contact with a parison 90.Pressure between slides 66 and 68 and bushing portion 52 seals the moldin preparation for blowing.

FIG. 11 illustrates the next stage in the forming process. In this stageblow pin 84 is extended vertically upwardly by means of a pistoncontrolling relative movement between blow pin 80 and core 82. Blow pin84 moves upwardly to engage the wall of parison 90 adjacent the uppersegments 62A and 64A of mold halves 62 and 64, sealing parison 90 at thetop. The interior of parison 90 is now sealed at both ends.

FIG. 12 shows the application of a blowing gas. Parison 90 is expandedoutwardly against mold 60 to complete the shaping of boot portion 50.This step is conventional and the techniques of blow moldingconventionally used are applicable to this step.

As shown in FIG. 13, blow pin 84 retracts within core 82 after the blowpressure is released. Mold halves 62 and 64 are opened and are moved tothe retracted position. Moving slides 66 and 68 to the retractedposition means that the outer surface of parison 90 adjacent the core 82is no longer confined. After slides 66 and 68 have been retracted, thecore 82 is withdrawn into support structure 80 by collapsing cylinder86. Fingers 88 are returned to the starting position, and mold halves 62and 64 open so that the completed part 10 may then be removed from themold. In this method, boot portion 50 has been formed with bushingportion 52 integrally therein. As shown in FIG. 14, once the boot 10 hasbeen removed from the mold, it is then trimmed for excess material ateither end to give the finished part as shown in FIG. 1.

As described above, the boot of FIG. 1 thus provides a skirt 16 whichhas a substantially cylindrical external configuration suitable foraccepting a hose clamp. The internal surface 18 of skirt 16 can beprovided with a convoluted or lobed shaped having one or moreprojections or lobes extending inwardly which are suitable forinteracting with a non-cylindrical surface of the object to which theboot is to be clamped.

It will be appreciated that using the method and apparatus describedherein it is possible to create flexible blow molded bellows-likeproducts having a non cylindrical internal surface. Any thermoplasticmaterial capable of being used in an injection molding operation may beused for the bushing portion 52 and any thermoplastic material capableof being used in a blow molding operation may be used for parison 90 inmaking boot portion 50. The parts 50 and 52 need not be made of the samethermoplastic material. It has been found that HYTREL (a trademark ofE.I. Du Pont De Nemours & Company) and SANTOPRENE (a trademark ofMonsanto Company) are suitable for blow molding boot portion 50 andSALFLEX (a trademark of Salflex Polymers Limited), and HYTREL aresuitable for injection molding bushing portion 52. In particular, thecombinations as shown in Table 1 have been found to be particularlysuitable combinations of materials from which to produce parts 50 and52.

TABLE 1 Preferred Material Combinations for Boot Portion and BushingPortion Boot Portion Bushing Portion SANTOPRENE 7028 SALFLEX 364SANTOPRENE 7028 SALFLEX 364 FOAM HYTREL 8136 HYTREL 8136 HYTREL 8136HYTREL 8136 FOAM HYTREL 8136 HYTREL 3548 FOAM HYTREL 8332 HYTREL 8136FOAM HYTREL 8332 HYTREL 8136 HYTREL 8136 SALFLEX 100 HS (TVPE) HYTREL8332 SALFLEX 100 HS (TVPE)

Advantageously, the method of the present invention enables productionof a boot with integral bushing, the bushing having unlimited lobe sizeand configuration or other features traditionally not available usingblow molding techniques. Referring to FIG. 15, the method of theapplicant's co-pending U.S. patent application Ser. No. 08/694,234, nowU.S. Pat. No. 5,300,205, is limited in the internal lobe size which itmay produce. Specifically, thickness a cannot exceed four (4) timesthickness b. Lobe size has no such limitation in the present invention.As shown in FIG. 16, thickness c may exceed four (4) times thickness d,if desired.

The combination of a boot and bushing in a one piece part allows foreasier and quicker installation of the boot onto a constant velocityjoint. The integral bushing and boot further has the advantage ofpreventing leakage of lubricant between the boot and bushing.Furthermore, a differing internal configuration, as compared to theexternal configuration gives great flexibility to the design tostrengthen blow molded parts and to accommodate different shapes inmating parts.

While the above description constitutes the preferred embodiments, itwill be appreciated that the present invention is susceptible tomodification and change without parting from the fair meaning of theproper scope of the accompanying claims.

We claim:
 1. A method of producing a thermoplastic protective boot foran automotive component which has a non-cylindrical surface, which bootis required to seal against said non-cylindrical surface of saidcomponent, by clamping of said boot against said non-cylindrical surfaceof said component, said boot having an integral bushing for sealingagainst said non-cylindrical surface of said automotive component whensaid boot is clamped against said component comprising: a) forming aboot element having a first portion, said first portion having agenerally cylindrical first wall with a generally cylindrical innersurface and a generally cylindrical outer surface, said first wallhaving a first diameter at said inner surface, wherein said boot elementis formed by blow molding; b) forming a bushing element having agenerally cylindrical second wall with inner and outer surfaces, saidouter surface of said second wall comprising a generally cylindricalsurface having a second diameter at said outer surface, said seconddiameter being approximately equal to said first diameter of said bootelement, said inner surface of said bushing element comprising anon-cylindrical sealing surface, said non-cylindrical sealing surface ofsaid bushing having a plurality of projections extending radiallyinwardly of said second wall so that said non-cylindrical sealingsurface conforms to said non-cylindrical surface of said automotivecomponent; each said projection extending only partiallycircumferentially around said non-cylindrical sealing surface andwherein said bushing element is formed by injection molding; c)positioning said bushing element so that said outer surface of saidbushing element will be substantially in contact with said inner surfaceof said boot element; and d) integrating said boot element and saidbushing element by spin welding said boot element and said bushingelement and thereby thermally fusing said elements together to seal saidouter surface of said bushing element to said inner surface of saidfirst wall of said boot element.
 2. The method of claim 1 wherein athird generally cylindrical wall is formed on said boot element at anopposite end of said boot element from said first wall.
 3. The method ofclaim 1 wherein said boot element and said bushing element are formed ofdifferent thermoplastic materials.
 4. The method of claim 1 wherein saidnon-cylindrical sealing surface of said bushing element is formed havingthree radially inwardly projecting lobes.
 5. The method of claim 1wherein a bellows portion is formed on said boot element intermediatesaid first wall and said third wall.